Layer stack

ABSTRACT

The invention is directed to a layer stack for the acceptance of a liquid having a suction layer ( 1 ) with high absorbency sufficing for sucking up the liquid from the edge of the layer stack into its middle and having a first storage layer ( 2 ) with low absorbency that is not sufficient for sucking up the liquid from the edge of the layer stack up to its middle between which an intermediate layer ( 3 ) composed of non-absorbent material and adjoining the first storage layer ( 3 ) is arranged, whereby a non-absorbent edge layer ( 7 ) is arranged at that side of the first storage layer ( 2 ) facing away from the intermediate layer ( 3 ), and whereby the intermediate layer ( 3 ) comprises through holes ( 4 ) whose plurality, size and distribution is selected such that some of the liquid suctioned up by the suction layer ( 1 ) can proceed via the holes ( 4 ) to the first storage layer and thoroughly saturate this. By foregoing a second suction layer, electrolytic capacitors with a significantly lower space requirement can be manufactured.

BACKGROUND OF THE INVENTION

The invention is directed to a layer stack for the acceptance of aliquid, which stack has a suction layer, a storage layer and anintermediate layer.

Layer stacks of the species initially cited are known from electrolyticcapacitors whereby the intermediate layer is fashioned as an anodelayer, and whereby a respective suction and a storage layer are arrangedat both sides of the intermediate layer. The two outermost layers of thelayer stack defined in this way are respectively covered by a cathodefoil. The suction or, respectively, storage layers are typicallyimplemented as paper layers, whereby the suction layer is a paper withlow density (<0.6 g per cm³) and the storage layer is a paper havinghigh density (>0.6 g per cm³). The paper layers are saturated with anelectrolyte. They therefore serve, first, as storage medium for theelectrolyte. Second, the paper layers also have the job of limiting thecurrent of the mobile ions present in the electrolyte and thus achievinga high dielectric strength of the electrolytic capacitor. Theelectrolytic capacitors are typically manufactured by winding theabove-described layer stack onto a winding mandrel, as a result whereofa cylindrical body arises. Particularly given electrolytic capacitorswith high capacitance (>1 mF), cylinders having a length of a fewcentimeters are formed. The electrolyte is introduced into the capacitorafter the winding of the capacitor. Due to the wound structure, theelectrolyte can only be supplied from the end faces of the woundcapacitor. Given electrolytic capacitors that exceed a specific length,the suction layer is required in order to transport the electrolytefrom,the end faces into the inside. Since the suction layer is alow-density paper and has great channels, it is not suitable forachieving a high dielectric strength. The storage layer implemented ashigh-density paper is therefore additionally inserted between anode foiland cathode foil. The dense paper comprises channels with a smallcross-section and is thus extremely well suited for achieving a highdielectric strength. Due to its low absorbency, however, the dense paperdoes not suffice as a sole intermediate layer between cathode foil andanode foil. The various layers described given the known structure leadto a high volume requirement of the electrolytic capacitor relative toits capacitance. Particularly where electrolytic capacitors are to bebuilt into miniaturized circuits, this is a considerable disadvantage.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to offer a layer stackthat, by foregoing one of the two suction layers, comprises a lowervolume requirement.

This goal or object is inventively achieved by a layer stack for theacceptance of a liquid that comprises a suction layer, a storage layer,an intermediate layer and an edge or boundary layer. The suction layerhas a high absorbency sufficing for sucking up the liquid from the edgeof the layer stack into a middle of the stack. The first storage layerhas a low absorbency that is not sufficient for sucking up the liquidfrom the edge of the layer stack up to the middle. An intermediate layeradjoining the storage layer is arranged between the storage layer andthe suction layer. The intermediate layer is composed of a non-absorbentmaterial and comprises through holes. These holes connect the upper orone side of the intermediate layer to the other side or underside andare selected such in terms of plurality, size and distribution that someof the liquid suctioned up by the suction layer that is applied at theedge of the layer stack can proceed via the holes of the intermediatelayers to the first storage layer and thoroughly saturate this firststorage layer. A non-absorbent edge or boundary layer is arranged atthat side of the first storage layer facing away from the intermediatelayer. The storage layer is thus saturated with liquid exclusively viathe holes in the intermediate layer.

The inventive layer stack has the advantage that a second suction layerarranged at the side of the storage layer can be eliminated by utilizingthe holes found in the immediate layer for saturating the storage layerarranged at that side of the intermediate layer facing away from thesuction layer. As a result thereof, the volume requirement of the layerstack is reduced.

The inventive layer stack can be especially advantageously fashioned asan electrolytic capacitor. To that end, a second storage layer isarranged at the side of the suction layer. Either the second storagelayer or the suction layer can be adjacent the intermediate layer, sincea good soaking of the first storage layer is achieved in both instances.The boundary or outer layer is fashioned as a first cathode layer. Asecond cathode layer is arranged at that side of the layer stack lyingopposite the first outer layer or cathode layer. When an electrolyte,i.e., for example, an organic liquid, which has ions that conduct theelectrical current is also employed, then the inventive layer stack canbe employed as an electrolytic capacitor. An electrolytic capacitordesigned in this way is especially space-saving due to the eliminationof a second suction layer.

Paper layers are especially advantageously utilized as the suction or,respectively, storage layer. These paper layers are simultaneouslysuitable for the electrical insulation between the anode layer and thecathode layer and for the limitation of the ion current. The ion currentis inhibited all the more greatly the thicker the paper layer betweenthe cathode layer and the anode layer is. A paper having a densityρ₁<0.6 g per cm³ is employed as the suction layer. A paper having such alow density comprises a multitude of channels that can suck a liquidapplied at the edge of the layer stack into the inside as a result ofcapillary action. A paper having a density ρ₂>0.6 g per cm³ ispreferably employed as the storage layer. Papers having this highdensity comprise only small channels that are especially suited forlimiting the ion current in the electrolyte and, thus, for contributingto a high dielectric strength of the electrolytic capacitor.

Further, it is especially advantageous to employ a paper as the suctionlayer wherein a line or wave structure is impressed. A paper providedwith a wave structure can, for example, look like a corrugated sheet. Asa result of the impressed lines or, respectively, waves, the absorbencyof the paper is enhanced, whereby the internal structure is largelypreserved. A paper having a high density ρ₂>0.6 g per cm³ can thereforebe employed. Such a paper then has the advantage that, on the one hand,it is suited as the suction layer and, on the other hand, comprises anenhanced dielectric strength, as a result whereof the thickness of thestorage layer can be reduced.

Moreover, a layer stack is especially advantageous wherein the suctionlayer and the second storage layer are the plies of a two-ply paper.Such a two-ply paper can, in particular, be advantageously employed whenthe layer stack is wound on a winding mandrel. The two-ply paper has theadvantage that it is does not tear as readily. An electrolytic capacitormanufactured of a layer stack wound onto a winding mandrel can berealized especially easily and quickly. Moreover, its capacitance can bevery easily set by means of the plurality of the turns. The employmentof a two-ply paper in band form for winding onto a winding mandrel isespecially advantageous because only one band then need be supplied forthe paper layer between anode foil and cathode foil.

The invention is explained in greater detail below on the basis of anexemplary embodiment and the Figures appertaining thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an inventive layer stack that is fashioned as anelectrolytic capacitor in a schematic cross-section; and

FIG. 2 shows an inventive suction layer having an impressed wavestructure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an inventive layer stack having an intermediate layer 3fashioned as anode. The anode is approximately 100 μm thick and iscomposed of aluminum and is provided on both sides with approximately0.2 through 1 μm thick oxidized aluminum. Particularly for theemployment of high-voltage electrolytic capacitors, holes 4 are etchedinto the intermediate layer 3 that connect the two sides of theintermediate layer 3 to one another. The etching of the holes 4 occurs,for example, by means of electrolytic etching in HCl. The holes 4 thatthereby arise have a diameter D between 1 and 3 μm and are thereforesuitable for the transport of a liquid from the upper side of theintermediate layer 3 to the underside of the intermediate layer 3. Anedge or boundary layer 7 that is fashioned as a first cathode layer isarranged at the underside of the layer stack. Just like the secondcathode layer 8 arranged at the upper surface of the layer stack, thecathode layer is fashioned as a 20 through 30 μm thick aluminum foilthat is covered with a thin aluminum oxide layer.

A respective storage layer 2, 5 is arranged at the boundary or surfacelayer 7 or, respectively, at the second cathode layer 8. This storagelayer is composed of paper having a density of approximately 0.8 g percm³. Such a paper can, for example, be manufactured of cellularmaterial. Due to its density, it is suitable for lending theelectrolytic capacitor a high dielectric strength. The two storagelayers 2, 5 must be saturated with an electrolyte. Since an applicationof the electrolyte is only possible at the edge of the layer stack, theelectrolyte must be transported into the inside of the layer stack bymeans of a suitable, further layer. A suction layer 1 is thereforearranged between the second storage layer 5 and the intermediate layer3, and the suction layer 1, as indicated by arrows, transports theelectrolyte from the edge of the layer stack into the inside and therebysaturates the second storage layer 5 with electrolyte. By utilizing theholes 4 in the intermediate layer 3, the first storage layer 2 can alsobe saturated with electrolyte with the assistance of the suction layer 1without having to arrange a further or additional suction layer at theunderside of the intermediate layer 3. The suction layer is composed,for example, of a paper having a density of 0.4 g per cm³ and has athickness of 55 μm. It can, for example, be fabricated of jute paper.The fiber spacings in a jute paper are so great that the paper isexcellently suited for the absorption of liquids. Since the suctionlayer 1 also delivers a contribution to the dielectric strength of thecapacitor, the second storage layer 5 can be selected somewhat thinnerat 40 μm than the first storage layer 2 at 65 μm. Due to the omission ofa second suction layer arranged under the intermediate layer 3, anelectrolytic capacitor with high capacitance and low space requirementcan be realized with the inventive layer stack.

FIG. 2 shows a suction layer 1′ into which a wave structure 6 isimpressed. As a result of the impressed waves, the suction layer 1′ hasan enhanced absorbency since the waves form a type of channel whereinfluid can be transported. Due to the increased absorbency, suctionlayers 1′ fashioned in this way can also be fabricated of denser paperhaving a density between 55 and 70 g per cm³. Such a suction layer 1′then has a higher dielectric strength, so that the second storage layer5 shown in FIG. 1 can be implemented thinner with an elimination of thecorresponding space.

The invention is not limited to the embodiments shown by way of examplebut is defined by the broadest description of the Summary of theInvention.

I claim:
 1. A layer stack for the acceptance of a liquid, said stackcomprising a suction layer with high absorbency sufficing for sucking upthe liquid from the edge of the layer stack into a middle of the stack;a first storage layer with low absorbency that is not sufficient forsucking up the liquid from the edge of the layer stack up to the middle;an intermediate layer composed of non-absorbent material being arrangedbetween the first storage layer and the suction layer; a non-absorbentboundary layer being arranged at that side of the first storage layerfacing away from the intermediate layer, and the intermediate layerhaving through holes whose plurality, size and distribution are selectedso that some of the liquid suctioned up by the suction layer can proceedvia the holes to the first storage layer and thoroughly saturate thefirst storage layer.
 2. A layer stack according to claim 1, whichincludes a second storage layer adjoining the suction layer.
 3. A layerstack according to claim 2, wherein the second storage layer adjoins theintermediate layer.
 4. A layer stack according to claim 2, wherein thesuction layer adjoins the intermediate layer.
 5. A layer stack accordingto claim 2, wherein the boundary layer is a first cathode layer, theintermediate layer is an anode layer and which includes a second cathodelayer adjoining the second storage layer so that the stack can be formedinto an electrolytic capacitor.
 6. A layer stack according to claim 5,wherein the intermediate layer is an aluminum foil covered withapproximately 0.5 μm thick aluminum oxide layer and the holes arechannels electrolytically etched in the aluminum foil with a diameterbetween 1 μm and 3 μm.
 7. A layer stack according to claim 5, whereinthe suction layer is a paper layer into which a wave structure isimpressed for increasing the absorbency.
 8. A layer stack according toclaim 5, wherein the suction layer and the second storage layer are theplies of a two-ply paper.
 9. A layer stack according to claim 5, whereinthe suction layer is a paper layer with a density ρ₁<0.6 g/cm³ and thefirst and second storage layers are paper layers with a density ρ>0.6g/cm³.
 10. A layer stack according to claim 5, wherein the suction layeris a paper layer with a line structure for increasing the absorbency.11. A layer stack according to claim 5, wherein the stack is wound ontoa winding mandrel.
 12. A layer stack according to claim 2, wherein thesuction layer is a paper layer with a density ρ₁<0.6 g/cm³ and the firstand second storage layers are paper layers with a density ρ₂>0.6 g/cm³.13. A layer stack according to claim 2, wherein the suction layer is apaper layer into which a wave structure is impressed for increasing theabsorbency.
 14. A layer stack according to claim 2, wherein the suctionlayer and the second storage layer are the plies of a two-ply paper. 15.A layer stack according to claim 2, wherein the stack is wound onto awinding mandrel.
 16. A layer stack according to claim 1, wherein thesuction layer is a paper layer with a density ρ₁<0.6 g/cm³ and the firststorage layers is a paper layer with a density ρ₂>0.6 g/cm³.
 17. A layerstack according to claim 1, wherein the suction layer is a paper layerinto which a wave structure is impressed for increasing the absorbency.18. A layer stack according to claim 1, wherein the suction layer is apaper layer with a line structure impressed therein to increase theabsorbency.
 19. A layer stack according to claim 1, wherein the stack iswound onto a winding mandrel.